Ultrasonic piezoelectric transducer with acoustic lens



June 23, 1970 R. E. JONES, SR 3,517,226

I ULTRASONIC PIEZOELECTRIC TRANSDUCER WITH ACOUSTIC LENS Filed March 25, 1968 2 Sheets-Sheet l INVENTOR.

Fey 6. J5/7e5, 5/:

##orney June 23, 1970 R. E. JONES, SR 3,517,226

ULTRASONIC PIEZOELECTRIC TRANSDUCER WITH ACOUSTIC LENS Filed March 25, 1968 2 Sheets-Sheet 2 INVENTOR.

Pay a. $1765, 5/:

United States Patent O US. Cl. 310-85 2 Claims ABSTRACT OF THE DISCLOSURE This application contains a technical disclosure of an electrosonic aparatus in the form of an acoustical lens Which includes a ceramic-type piezoelectric transducer mounted on a formed silicate incursion block of hemispheric shape, which is in turn mounted in the center of a semi-hemispheric radiating plate, thereby permitting radiation through the atmosphere of ultrasonic frequencies in a non-directional pattern. There is further disclosed the manner by which this lens structure, in combination with specialized electronic circuitry generating erratic and harmonic filled ultrasonic frequencies, may be utilized to repel and destroy vermin such as rats, mice and bats. Utilization of the disclosed acoustical lens system as a radiator for audio frequencies in combination with high fidelity and stereo systems is also described.

BACKGROUND OF THE INVENTION This invention relates to improved electrosonic apparatus and particularly to such apparatus utilizing piezoelectric transducers in association with structures and circuitry for generating and radiating sonic vibrations. More particularly, this invention relates to the generation and radiation of energy in the form of ultrasonic waves through a gaseous medium in a non-directional pattern by means of an acoustical lens system.

The radiation of sonic waves, particularly waves of ten kilocycles and higher in a broad pattern is often much desired. For example, sonic waves having frequencies within this range may be used for repelling and/or exterminating rodents, insects and other undesirable vermin, but for such purposes it is essential that the sonic Waves be radiated to effectively cover a wide area. Similarly, effective wide area radiation of sonic waves is especially desirable in connection with high fidelity and stereo music systems, and this is particularly difiicult to accomplish with the higher frequency sonic waves such as those normally radiated with tweeter components of such systems.

While various types of apparatus are known for the generation of sonic waves in the range of ten kilocycles and higher, many of these devices are relatively low in eificiency in the transfer of such vibrational energy through a gaseous medium, such as the atmosphere, besides being inadequate for wide area radiation. Certain of these devices utilize mechanical means for the desired purposes, such as fluid or air operated resonators, and other such devices operate on magnetostrictive principles. Still others utilize various types of piezoelectric transducers arranged in various types of mounts. The prior art also shows high speed rotators creating shock waves to kill insects and other vermin.

SUMMARY OF THE INVENTION The invention described herein is directed to the solution of problems encountered in prior art devices by the provision of electronsonic apparatus in the form of an acoustical lens whereby vibrational energy may be radiated through a gaseous medium with high efficiency over a wide area.

More specifically an object of this invention is the provision of apparatus wherein a piezoelectric transducer is associated with a mounting structure of such a nature and in such a manner as to increase the effectiveness of the transfer of sonic and supersonic waves generated thereby, to and through the atmosphere non-directionally.

Even more specifically, an object of this invention is to provide improved generation and radiation of sonic frequencies of the order of ten killocycles and higher for various purposes such as vermin repelling and destroying systems and high fidelity sound systems.

Another object of this invention is to provide a novel combination of radiating structure and electronic circuitry whereby the injurious and destructive properties of ultrasonic waves on rodents such as rats is greatly intensified.

Additionally, the provision of apparatus specifically directed to the wide angle non-directional radiation of sonic waves of audio frequencies is a further object of the invention herein described.

Other objects of this invention will be apparent to those skilled in the art from the following detailed description of this invention in certain preferred embodiments and from reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is shown in the drawings, wherein:

FIG. 1 depicts a side view of the major structural components of this embodiment, with a portion of one component thereof cut away to more clearly show other components thereof;

FIG. 2 is a top or plan view of certain of the major components as seen along the lines 22 of FIG. 1 after separation of these components from other of the major components shown in FIG. 1;

FIG. 3 is an enlarged sectional view of a portion of the major components of FIG. 2, as seen along the lines 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view, as seen along lines 4-4 of FIG. 1, showing one of the plurality of means for mounting the major components shown in FIG. 2 to the remaining components shown in FIG. 1; and

FIG. 5 is a schematic diagram of the electronic circuit forming one of the major components of a preferred embodiment of the invention herein described, certain portions of which circuitry are depicted in FIG. 1 as enclosed in a housing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is first made to the drawings wherein is shown the major components of a preferred embodiment of the electrosonic apparatus of this invention, these components consisting of a radiating plate 10, and in incursion block 11, a piezoelectric transducer 12, a support plate 13 and electronic circuitry 14 encased within housing 15. As more clearly seen in FIG. 3, the piezoelectric transducer 12 is shown as mounted within a recessed cavity 16 of the incursion block 11. The piezoelectric transducer 12 is shown as having a pair of electrodes 17 and 18 to which are connected electrical leads 19 and 20 respectively, these being encased in insulating sleeves 21 and 22. The electrical leads 19 and 20 are further connected to the electronic circuit 14, as more fully disclosed in connection with the description of the electronic circuitry of FIG. 5 hereinbelow. Mounted in close association with the piezoelectric transducer 12 and on the side thereof opposite to the mounted incursion block 11, is a reflection suppressor shown as 23, which in the present embodiment consists of an aluminum disk which is provided with a circular opening centrally positioned therein for the passage therethrough of the electrical lead 19. In a preferred embodiment, as shown more particularly in FIG. 3, the piezoelectric transducer 12 is bonded to the incursion block 11 and to the reflection suppressor 23 by means of a suitable cement 25, the piezoelectric transducer 12 and the leads 19 and 20 being embedded therein within the recessed cavity 16. Cement 25 also serves to bond the reflection suppressor 23 to the transducer 12.

The piezoelectric transducer 12 of the preferred embodiment herein described is one of the type generally known as ceramic-type solid solution of lead-titanate and lead-zirconate. The thickness thereof which controls the resonant frequency of such a transducer, is chosen to. give a prime resonant frequency in the ultrasonic range, i.e. a range of frequencies ten kilocycles and higher. Differing thicknesses of the piezoelectric transducer may be chosen for differing applications such as vermin destroying or repelling systems, and high fidelity music systems as will be more fully described hereinafter.

The incursion block 11 of the preferred embodiment herein described is formed of silica material in hemispherical shape and having a depression or recessed cavity 16 on the flat side thereof for mounting the piezoelectric transducer 12 therein. In FIGS. 1 and 3, the incursion block 11 is shown as having a small circumferential beading or ring 26 formed integrally of the silicate material, positioned approximately in line with the bottom of the recessed cavity 16, the purpose of which is to serve as a retaining ridge on the incursion block for the radiating plate which is secured to the incursion block 11 by cement 27.

The radiating plate 10 of the preferred embodiment here shown is semihemispherical in shape, formed of stainless steel and having a circular opening in the center thereof for mounting the incursion block therein. The concave radiating surface of this plate is highly polished to obtain maximum transfer of mechanical energy to gaseous medium. The outer perimeter of the radiating plate 10 is formed in the shape of a circular band 28, having a rolled edge to which band are secured a plurality of mounting means 29, shown as coil springs in FIGS. 1 and 4, for connecting the radiating plate 10 to the sup port plate 13 while permitting free vibration of the radiating plate and preventing dampening of the sound emission therefrom. Free forward and reverse movement of the radiating plate is thus allowed.

In the embodiment herein described, the support plate 13 is shown as a circular disk provided with screws 30 and nuts 31 by which the springs 29 are fastened thereto. Secured to the support plate 13 is shown the housing for the electronic circuitry, and to which the component parts of this circuitry, as schematically shown in FIG. 5, may be mounted. A pilot light 32 is shown in FIG. 1 as being mounted between the support plate 13 and the radiating plate 10, projecting outward therefrom to indicate, when lighted, that the electronic circuitry 14 is activated, the pilot light being connected to the electronic circuitry by means of leads 33 and 34. Also shown as mounted upon the support plate 13 is a fuse holder 35 containing therein the fuse 36 of the electronic circuitry 14.

While various means may be utilized for mounting the support plate as may be desired, there is shown in FIG. 1 such means consisting of the arm 37 to which there is secured in adjustable relationship another arm 38, adjustment of the relationship of these arms being accomplished by means of a screw 39 and thumb nut 40. Arms 37 and 38 may be provided, if desired and as shown, with inter-connecting ducts therethrough by which a cable 41 carrying a source of power, for example 115 volts of alternating current, may be led to the electronic circuitry 14. In FIG. 1, the arm 38 is shown as terminating in a clamping arrangement consisting of the angle arm 42 having a base arm 43 through which passes a threaded rod 44 to which is attached another angled arm 45. by rotation of the knob 46 at the other end of the threaded rod 44, the angled arm 45 may be brought into proximity to the angled arm 42 to secure the entire structure on some support 47 at whatever angle and in whatever position may be desired.

With reference now to FIG. 5, there is shown an electronic circuit 14 for generating ultrasonic frequencies, generally comprising a power supply 48, an oscillator 49 and an amplifier 50, the output of which is connected through a step-up transformer 51 and leads 19 and 20 to the electrodes 17 and 18 respectively of the piezoelectric transducer 12. Whilethe components of the electronic circuitry 14 may be varied to obtain the electrical energy having certain desired characteristics, as described below, and which is to be fed to the piezoelectric transducer 12, the components shown in FIG. 5 and their arrangement, as now further described, comprise a preferred embodiment of this invention.

The electronic circuitry schematically shown by FIG. 5 comprises a source of power 51 preferably consisting of alternating current which is fed into the power supply 48 through leads 52 and 53. A fuse 36 is shown as inserted in the lead 52 to protect the source of power 51 from overloads or shorts which might occur as a result of malfunctioning of the electronic circuitry 14. The pilot light 32, previously referenced, is shown as connected to the' leads 52 and 53 by leads 33 and 34 respectively.

The power supply of this preferred embodiment is a half wave rectifier consisting of a silicon diode rectifier 54, to the cathode of which lead 52 is connected and to the anode of which by means of leads 55 and 56 one side of a filter capacitor 57 is connected. Lead 53 from the source of power 51 is connected to one side of resistor 58, the other side of which is connected by leads 59 and 60 to the other side of filter capacitor 57. Through these components of the power supply 48, there is obtained a current which is not pure direct current having been only partially rectified, as is desired for certain purposes of this invention, as more fully explained below.

The output of the power supply 48 is fed into the oscillator circuit 49 which consists, in the preferred embodiment shown, of the transistor 61, the resistor 62 and the capacitor 63. Leads 64 and 65 connect the resistor 62 and the capacitor 63 respectively to lead 55 from one side of the power supply while leads 66 and 67 connect the emitter of the transistor 61 and the other side of the capacitor 63 respectively to the opposite side of the power supply, i.e. lead 59. The center tap of the resistor 62 is connected with the base of the transistor 61 by means of lead 68. Capacitor 63 serves as a bias voltage capacitor, the leakage therefrom establishing at random the frequency of the 'OSCIIIatOI within the range of from ten to eighty kilocycles. This capacitor has a low-accuracy discharge rating and will therefore discharge at varying intervals, forcing the oscillator transistor 61 to respond to the varying discharge cycles of the bias network. The oscillator circuit 49 is therefore seen as an unstable oscillator.

Connected to the collector element of the transistor 61 by lead 69 are resistors 70 and 71. The opposite end of the resistor 70 is connected by lead 72 to the base of the amplifier transistor 73, the emitter of which is connected to lead 55 from the power supply 48. The collector of the transistor 73 is connected by leads 74 and 75 to one side of each of the capacitors 76 and 77, the other sides of which are connected by leads 78 and 79 respectively to the opposite end of resistor 71 and to the center tap of resistor 62. By this circuit arrangement, a feedback and clipping network is formed for the oscillator circuit in such a manner that resistor 62 and capacitor 77 limit the oscillator circuit output at a desired low frequency e.g. twenty kilocycles, while resistor 71 and capacitor 76 limit the oscillator output at a desired high frequency e.g. eighty kilocycles.

Because of the only partially rectified output of the power supply 48, the amplifier stage of the electronic circuit is also modulated by an impressed alternating current, thus resulting in a three to twelve cycle modulation of the signals received by the amplifier from the unstable oscillator circuitry.

From the amplifier 50 of the electronic circuit, the output pulses are fed to a coupling circuit with the transducer 12. In FIG. this coupling circuit is shown as a step-up transformer 80 one end of the primary winding of which is connected to lead 76 while the other end of this winding is connected by lead 81 to lead 59 of the power supply 48. The secondary winding of the step-up transformer 80 is connected by leads 19 and 20 to the electrodes 17 and 18 of the piezoelectric transducer 12 as heretofore described. In the embodiment shown, the stepup transformer 80 is one having a step-up ratio of approximately nine to one and when used in the circuit as herein described gives approximately three hundred and fifty volts at one hundred milliarnps to the piezoelectric transducer 12.

MODES OF OPERATION Exemplary utilization of the structure and circuitry hereinabove described for repelling and/or destroying rodents such as rats, mice and bats in enclosed areas where food and other similar destructable items may be stored, is now described in detail.

A lead-zirconate-titanate ceramic composition in the form of a disk having a diameter of approximately 1.5 inches and a thickness of approximately 0.25 inch, and having a prime resonant frequency of 23.5 kilocycles is utilized as the piezoelectric transducer 12. This transducer, having fused silver electrodes 17 and 18 on each face thereof and electrical leads 19 and 20 connected to these electrodes, is cemented, preferably with epoxy cement 25, within a recessed cavity 16, approximately 0.5 inch in depth, in a formed silicate incursion block 11 which is hemispherical in shape and is approximately 3.25 inches in diameter. An aluminum disk reflection suppressor 23 having a diameter and thickness at least equal to those of the transducer is cemented to the electrode bearing face 17 of the lead-zirconate-titanate transducer opposite the electrode bearing face 18 cemented to the incursion block, again preferably using epoxy cement, the lead from this face of the transducer being brought out through a hole in the center of the aluminum disk.

The components of the electronic circuit 14 described above are chosen with electrical values such that frequencies ranging from approximately 20 kilocycles to 80 kilocycles are obtained therefrom, this output being applied to the lead-zirconate-titanate transducer 12 through the step-up transformer 80. Because of the use of only partially rectified alternating current and of the characteristics of the bias voltage capacitor, as previously described, the output of the electronic circuit will be highly unstable and in the form of high intensity erratic pulses resulting from the modulation thereof by an impressed alternating current of the order of between 3 and 12 cycles derived from the 60 cycle alternating current source. Application of such an output by means of a coupling circuit, e.g. a step up transformer to the transducer having a prime resonant frequency of 23.5 kilocycles results in the generation by the transducer of a sound pattern which is extremely erratic, rich in distorted harmonics and modulated by a sub-sonic cycle tone at random intervals varying from three to sixty milliseconds in duration. The erratic pulses in the sub-sonic range of frequency impresses a pistol shot effect upon the carrier frequencies, which, by measurement, have been found to peak at approximately 23.5 kilocycles, 32.5 kilocycles, 47.0 kilocycles and 65.0 kilocycles, these frequencies resulting from the interaction of the output of the osci1la- 6 tor-amplifier circuitry with the resonant frequency and harmonic frequencies of the piezoelectric transducer.

The erratic pulses and varying frequencies of the output of the transducer as thus generated has been found to have devastating effect upon vermin and rodents. While ultrasonic frequencies have heretofore been used to repel rodents, it has been found that rats and mice quickly adapt themselves to repeated and regular occurrences of signals at fixed ultrasonic frequencies and that while initially repelled, vermin of this type generally reappear and are henceforth immune to such signals. However, signals having the characteristics of those produced by the method herein described are found to be very effective in permanently repelling vermin and rodents, and in many cases causing their destruction.

The transfer of mechanical energy in the form of sonic and ultrasonic signals having the peculiar nature of those produced in the manner just described has been found to be particularly effective through the use of the specially designed incursion block which has been described above. Normally sonic signals at frequencies above 18 kilocycles are highly directional but by utilizing this novel type of incursion block, the sonic signals are dispersed in a plane, eliminating nodes and standing waves in any one direction. Additionally, an incursion block having the characteristics herein described provides a minimal reverse reflection in comparison with the 180 forward emission. The purpose of the reflection suppressor 23 previously described is to redirect this reverse reflection back to the incursion block thereby intensifying the forward emission.

By utilizing a stainless steel semi-hemispherical radiating plate 10 of approximately 10.5 inches in diameter having its radiating surface highly polished, there is obtained a maximum reflection-dispersion of all of the resonant, and harmonic ultra-sonic and sub-sonic energy which have been generated by the transducer 12 and transferred to the incursion block 11. The incursion block is mounted in a 3.25 inch circular opening in the radiating plate, epoxy cement being used to secure the incursion block to the plate, the incursion block being provided with a circumferential beading or ring 26 as shown in FIGS. 1 and 3.

In order that the radiating plate may fully transfer to the atmosphere the mechanical energy in the form of the erratic pulses of sonic frequencies transferred thereto by the incursion block, this plate is spring mounted to a support plate which may in turn be provided with clamping means as heretofore described to support the entire electrosonic apparatus in whatever manner may be desired. For the specific purpose of repelling and destroying vermin and rodents, it has been found advantageous to support the electrosonic apparatus from the ceiling in a roomor enclosed area from which it is desired to eliminate the vermin and/ or rodents.

Exemplary of a different utilization of the electrosonic apparatus herein described is its use as a component of high fidelity and stereo music systems in the following manner.

A piezoelectric transducer, for example a lead-zirconatetitanate composition, having a thickness such that its prime resonant frequency is in the order of 15 kilocycles may be mounted upon an incursion block similar to that described herein with the connections from the electrodes thereof connected to the output of an amplifier forming a normal component of the high fidelity or stereo music system. In this manner, audio signals in the ultra-sonic range, ie those having a frequency of between approximately 10 and 20 kilocycles are transferred from th transducer to the incursion block and thence to the radiating plate from which they are radiated through the atmosphere with a forward emission over a 360 angle in the same manner as has been described hereinabove. Here again an aluminium disk reflection suppressor may be utilized as described above but the electronic circuitry as described in connection with FIG. need not be utilized, this being replaced by other electronic circuitry, for example that of the high fidelity or stereo system with which the acoustical lens herein described is being utilized.

It will thus be seen that the electrosonic apparatus herein described may be utilized as an acoustical lens in various manners. Hence, while only certain preferred embodiments of this invention have been shown and described by way of illustration, many modifications will occur to those skilled in the art andit is, therefore, desired that it be understood that it is intended in the appended claims to cover all such modifications that fall within a true spirit and scope of this invention.

What is claimed as new and what is desired to secure by Letters Patent of the United States is:

1. An acoustical lens system for Wide angle radiation of ultrasonic waves which comprises a lead-zirconatetitanate piezoelectric transducer having a prime resonant frequency in the ultrasonic range, an incursion block formed of silica material in hemispherical shape and having a recessed cavity in the flat side thereof for mounting said transducer therein, and a semi-hemispherical radiating plate having a circular opening in the center thereof for mounting therein said incursion block.

2. An acoustical lens system as recited in claim 1, including a reflection suppressor mounted on the side opposite that side of said piezoelectric transducer upon which said incursion block is mounted and having dimensions which are at least equal to those of said transducer.

References Cited UNITED STATES PATENTS MILTON O. HIRSHFIELD, Primary Examiner M. O. BUDD, Assistant Examiner US. Cl. X.R. 

